1. Field of the Invention
The present invention relates to an automatic constant-speed cruising control apparatus used for automatically controlling a traveling speed of a vehicle to a certain preselected value.
2. Description of the Prior Art
As such an automatic constant-speed cruising control apparatus for controlling automatically a vehicle speed to a preselected value, an apparatus disclosed in Japanese Patent Application First publication (Kokai) No. sho 63-57341 has been known, for example.
In the automatic constant-speed cruising control apparatus of this kind, according to an off-operation after the on-operation of a set switch, a vehicle speed at the time of the off-operation is stored in a vehicle speed memory as a desired cruising speed. An actuator drive signal is transmitted to an actuator in response to the difference between an actual vehicle speed and the desired cruising speed stored in the vehicle speed memory, and the vehicle speed is controlled by driving a throttle valve of the vehicle through the actuator so as to coincide the actual vehicle speed with the stored desired cruising speed, consequently the vehicle travels automatically at the constant cruising speed.
When a cancell switch or a brake pedal is operated during the automatic constant-speed cruising, the constant-speed cruising of the vehicle is cancelled.
If a resume switch is operated in this state, resume control is started and the vehicle speed is resumed to the previous desired cruising speed stored in the vehicle speed memory by transmitting the drive signal to the actuator. The resume control is carried out by using acceleration constant K', acceleration .alpha. and difference .epsilon. (.epsilon.&lt;0) between the actual vehicle speed and the cruising speed stored in the vehicle speed memory, constant acceleration control is carried out under control output time (T=.alpha.-T.alpha.) which is a function of acceleration .alpha. of the vehicle and objective acceleration T.alpha. when decision means judges (K'.multidot..alpha.+.epsilon.) to be not larger than 0 (zero), and switching over is done from the constant acceleration control to constant speed control when the decision means judges (K'.multidot..alpha.+.epsilon.) to be larger than 0 (zero).
In another automatic constant-speed cruising control apparatus, resume control is also known, such that the constant acceleration control is carried out when the difference .epsilon. between the preselected desired cruising speed and the actual vehicle speed is larger than predetermined value A, and the constant acceleration control is switched over to the constant speed control at a point of time when the vehicle speed difference .epsilon. becomes not larger than the predetermined value A through the constant acceleration control.
In the aforementioned automatic constant-speed cruising control apparatus so designed as to change over the constant acceleration control to the constant speed control during the resume control by judging whether (K'.multidot..alpha.+.epsilon.) is larger than 0 or not, however, there is a fluctuation in the changeover time from the constant acceleration control to the constant speed control, whereby dispersion is sometimes produced in the time required for concentrating the actual vehicle speed to the stored desired cruising speed. Therefore, there is a problem since there is the possibility that overshooting of the vehicle speed occurs and deterioration is caused in the control characteristics.
In the other automatic constant-speed cruising control apparatus designed so as to change over the constant acceleration control to the constant speed control in the resume control by judging whether the vehicle speed difference .epsilon. is larger than the predetermined value A or not, it is necessary to carry out tuning in order to regulate the value A for every individual vehicle because it takes a prolonged time for concentrating the actual vehicle speed to the memorized desired cruising speed owing to overshoot or so in the vehicle excellent in the power performance unless the value A is changed between the vehicle excellent in the power performance and the vehicle not so. Accordingly, there is a problem in that an increase of man-power required for manufacturing the apparatus may be caused by the tuning of the value A.